I think I understand- you are measuring the induced voltage in the chassis from the transformer. Its sort of a proxy for radiated flux. None of the transformers you measured have measures for reducing external fields, although those do have mixed results.

The flat pack will have the highest radiated fields since it has a less efficient magnetic circuit. However it may have higher isolation between input and output electrically. The toroids tend to have the highest coupling between input and output.

Richard, surely you exaggerate. I sell audio products all over the world and they are not listed by UL. It would be impossibly expensive to do so. However, it could well be that somebody, somewhere, will INSIST on a UL listing of the CTC Blowtorch, but I just won't sell them one, in that case.

Dick, there is a trace in all the plots with the transformers without power. This gives a good idea as to the baseline for measurement artifacts.

A question I have for Ed, thanks by the way for doing this interesting work, is the following. It appears that transformers that are closest to the torroid topology perform best on this test, which makes sense if you think about the orientation in which the magnetic field is contained. However, the results may be very different on different axis. You know what rotating a transformer may do to reduce hum in an actual enclosure.

Dick, there is a trace in all the plots with the transformers without power. This gives a good idea as to the baseline for measurement artifacts.
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I can see that.

Next would be what to do to minimise the new unwanted induced freqs that are shown... . Starting by using the best xfmr with minimum radiated field. Various forms of shielding methods have worked well.

Richard, surely you exaggerate. I sell audio products all over the world and they are not listed by UL. It would be impossibly expensive to do so. However, it could well be that somebody, somewhere, will INSIST on a UL listing of the CTC Blowtorch, but I just won't sell them one, in that case.

Nope... from experience. You take your chances.

For DIY who dont actually know how to make a safe built product should be careful and use UL parts on ac line voltage parts.

Richard, you are most probably right about the UL listing. I did have one close call, where a distributor, after ordering perhaps 10 Blowtorches tried to get one at deep discount, in lieu of me getting a UL listing. Kind of like blackmail.
However, it is almost impossible to afford the listing of a custom design, and it is kind of useless, IF you know what you are doing. However, I would get the appropriate UL standard and make sure that I met their requirements. That is all they are going to do, anyway, but unfortunately, they have to make a living and things get drawn out. Trust me, I have seen it happen, and I have heard some horror stories about Dyna trying to get listed.

Richard, surely you exaggerate. I sell audio products all over the world and they are not listed by UL. It would be impossibly expensive to do so. However, it could well be that somebody, somewhere, will INSIST on a UL listing of the CTC Blowtorch, but I just won't sell them one, in that case.

See wikipedia ---> China_Compulsery_Certification. Been in effect since 2003. Ditto EU. If you import a low enough volume you could apply for an exemption.

That has nothing to do with DIY building though. Be safe and use qualified parts for the high voltages parts of the build.... from the plug and cord thru to the transformer and any filters, fuses, switches, wire used in between.

-RNM

Last edited by RNMarsh; 10th March 2013 at 06:09 AM.
Reason: Be safe when building -

Richard,
I am sure you are correct about getting a product certified if you want to sell into the international market and I could imagine the lawsuits here in the USA if someone got hurt or there was a fire due to a product not meeting UL requirements. I might not be a circuit designer but I do have a good idea what not to do when testing live equipment. I used to have to trouble shot some of my own equipment which were mostly 480V three phase and one machine was rated 480v, three phase, 85kw draw by itself. Don't make a mistake while working on something like that, you only get one mistake and then you don't have to worry about that ever again!